Celebrate! 2015 International Year of Soils

December 5, World Soil Day

Food and Agriculture Organization

of the United Nations

www.fao.org/soils-2015/en/ See also

www.SSSA.org/IYS

www.SSSA.org/IYSwww.fao.org/soils-2015/en

Start with the Soil: The Groundwork for Healthy Plants

Stephanie Murphy, Ph.D. Rutgers Soil Testing Laboratory

What is Soil?

“Soils are developed; they are not merely

an accumulation of debris resulting from

decay of rock and organic materials…

In other words, a soil is an entity – an

object of nature which has characteristics that

distinguish it from all other objects in nature.”

Millar & Turk, 1943

Factors of Soil Formation • Parent Material

• Biological activity

• Climate processes

• Topography

• Time

What is Soil?

Most definitions refer to soil as a media for plant growth

The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants. Soil Science Society of America

“…soil is the link between

the rock core of the Earth

and the living things

on its surface…”

Simonson, 1957

Soil: plant growth medium

Soil provides:

• Storage of water

• Bank of nutrients

• Physical support, anchoring roots

• Diffusion if gases (O2, CO2, etc.)

Soil: Habitat for Organisms

• Soil is an ecosystem; soil is “alive”...

US

DA

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Soil: Regulator of water

The Hydrologic Cycle

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usgs.gov Soil-Plant-Atmosphere water cycle

http:usgs.gov

Soil: Recycler of raw materials

Organic

Inorganic

synthesis in plant

decomposition in soil

H2O, Ammonium, Carbon dioxide Mineral nutrients

Fungi c/o chestofbooks.com

Bacteria c/o etc.usf.edu

Feldspar sci-culture.com

2:1 clays wsu.edu

www.watershedmanagement.vt.gov

Soil: Engineering medium

• foundation of roadbeds, buildings, and other infrastructure

• Berms, bioretention basins, and other constructed “root zones” are engineered plant media

gvt.net

www.watershedmanagement.vt.gov

What is Soil?

Components of soil – mineral particles

(inorganic)

– organic matter (derived from organisms)

– water (H2O and dissolved salts)

– air (N2, O2, CO2, H2O vapor, etc.)

Brady & Weil, 1999

Soil is 3-D!

Soils change across the landscape

soil profile - a vertical cross-section of soil exhibiting its horizontal layering

soil horizon - layer approximately parallel to the soil surface

Horizons result from soil-forming processes, including: additions, losses, transformations, translocation

Characterizing soils

• Measuring various properties of soils to understand processes and effects of management

• Features of horizons in a soil profile allows classification & mapping

• Soil properties are measured as indicators of soil quality

Soil Texture

Particle-size distribution

Sand = 0.05 to 2 mm

Silt = 0.002 to 0.05 mm

Clay < 0.002 mm

Larger than 2mm: not-soil; gravel, cobbles, stones, etc.

Soil Texture influences…

• pore space, soil density • soil structure

• water retention, available water • aeration

• water infiltration

• cohesion, plasticity

• shrink-swell character

• microbial activity

• fertility, productivity

• runoff, erosion

• temperature

• pH (acidity)

• o.m. content

• management

Between particles: Pores

Pores - containing water and/or air Thin section of soil

Two main classes of pore size

Macroporosity -

• responsible for transmission

of water & air (aeration)

Microporosity -

http://edafologia.ugr.es/iluv/media/hor4.gif • responsible for retention of

water against the force of gravity

http://edafologia.ugr.es/iluv/media/hor4.gif

Soil structure

-the arrangement of soil particles into aggregates

Brady & Weil, 1999

Soil aggregates are held together by humus, microbial gums, clays.

Types of Soil Structure

Granular Prismatic

Blocky Platy

Structure alters pore size distribution of a soil.

Good soil structure promotes water and air movement into and through soil,

and allows unobstructed root growth.

Soil organic matter

USDA-NRCS

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• Organically-derived component of soil

• “Active” organic matter – relatively fresh

• “Humus” – highly decomposed fraction

• Strongly influences many soil properties

• In “upland” soils, amount and distribution – Compare to organic soils

http://nesoil.com/images

Plant Residue to Soil Humus

Bra

dy &

Weil,

1999

Soil Organic Matter

elemental analysis:

C 50-60%

N 5%

P 0.6-1.2%

S 0.5%

C:N ratio=10:1

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www.soils.wisc.edu/virtual_museum/som/index.html

Soil Organic Matter Effects

Characteristic Effect in soil

Adsorption of humus to soil Aggregation of particles particles (soil structure development,

tilth, porosity, drainage)

High water-holding capacity More plant-available water

Contains Nitrogen, Source of plant nutrients, Phosphorus, Sulfur, etc. short- and long-term

Ion exchange capacity: Nutrient retention, Cations & Anions buffering capacity

Contains carbon Energy source for microbes, storage of C

Chelation of metals Increase bioavailability of certain mineral nutrients

Adsorption of organic Reduced effectiveness of molecules certain pesticides

Black color Heat absorption

Benefits of Soil Carbon

Water & Nutrient Holding S

oil Q

uality

Aggregation &

Infiltration Productivity

Air & Water Quality; Wildlife Habitat

Soil Carbon

Time USDA-NRCS

Nutrient Supply

Plant content • “Essential nutrients” –

necessary for the

growth and reproduction

of plants

• From air or water: – C, H, O

• From soil:

– Macronutrients N, P, K, Ca, Mg, S

– Micronutrients Cu, Mn, Zn, B, Fe, Mo

N 2-5%

P 0.2-0.5%

K 1-5%

Ca 0.1-1%

Mg 0.1-0.4%

S 0.1-0.3%

Fe 50-250 ppm

Zn 20-100 ppm

Mn 20-300 ppm

Cu 5-20 ppm

B 10-100 ppm

Mo 0.1-0.5 ppm

Bennett, 1993

Concept of the limiting factor

Plant production is constrained by the most-limiting growth factor

Potential limiting factors

essential elements

pH

light

water

temperature

oxygen

CO2 etc.

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Increasing the level of a non-limiting factor will not improve production

Degree of Acidity [H+] or Alkalinity

an important plant-growth factor that can be managed

Optimum for most plants: pH 6.5 to 6.8

Acid-loving plants: adapted to pH 4.5 to 5.5

Soil pH

Alkaline

Neutral

pH 7 [H+] = 10-7

Acidic

Bra

dy &

Weil,

1999

Effects of Soil pH

• Soil pH affects nutrient availability (solubility)

• Aluminum toxicity damages roots at low pH

• Direct damage also possible at high pH

Brady & Weil, 1999

Soil Ecology and Plant Nutrition

• Plants are the dominant primary producers in soil.

• Nutrient cycling and sustainable systems depend on soil organisms.

• Plant residues etc. broken down to release (recycle) nutrients.

• Symbiotic relationships contribute to plant nutrition. – Mycorrhizae

– Rhizobia/Legume

– other

• Diversity helps maintain balanced populations.

www.ecoplexity.org

http:www.ecoplexity.org

“Topsoil”

• The “top” of an undisturbed or cultivated “native” soil? – Depth ranges widely

– Characteristics of native soils vary according to: parent material, climate, topography, vegetation and other organisms, and time (degree of aging)

– Soil texture, organic matter content, pH, nutrients, structure (aggregation)

Where does the “topsoil” come from?

• No legal definition: how do you know what you’re getting?

• Much of the “topsoil” commercially available today for landscaping use is “manufactured”.

Rutgers Soil Testing Laboratory http://njaes.rutgers.edu/soiltestinglab

• Basic fertility test

• Topsoil evaluation NJAES Publications: http://njaes.rutgers.edu/pubs

Fact Sheet 901

Rutgers Resources for Soil Evaluation

Recommended Topsoil Properties for Landscaping Use

pH: most : acid-loving

6.0 to 6.8 5.0 to 5.5

Organic content 1.5% to 10%

Sand 40% to 65%

Fines 5% to 20% clay

http://njaes.rutgers.edu/soiltestinglabhttp://njaes.rutgers.edu/pubs

Soil problems in sub/urban areas

• – Amount of topsoil returned

– Quality and Quantity matter!

– Structural deterioration

• Fertility

• Water-holding capacity

• Compaction

• Erosion

• De-icing salt contamination

•

Removal/disturbance/mixing of soil horizons

120 cubic feet 500 cubic feet 1000 cubic feet ca

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(in cold climates)

Underlying hydrology

www.extension.umn.edu/garden/landscaping/implement/soil_berms.html

Compaction

• A change in soil structure

due to pressure -USDA-NRCS

resulting in decrease of

total soil porespace volume

• Changes pore size distribution

• Degree of damage depends on load pressure, soil water content, soil texture

Foot traffic Bulk Porosity Infil-

under grass Density Total Macro- tration

g/cm3 % % in/h

None 1.09 58.9 33.1 3.0

Moderate 1.47 44.6 19.2 1.13

Heavy 1.80 27.9 3.0 0.28

Consequences of compaction

• Reduced movement of air and water

• Greater retention of water

• Build-up of toxic gases

• Root growth may be limited,

function & viability compromised

• Alters microbial population/activity

What’s underneath matters!

• Be concerned about what the topsoil is going over – Compacted subsoil? Discontinuity of texture? Inhibiting water movement and root penetration

• Water-storage ability and drainage, groundwater recharge

Developed vs. Natural Landscape

Compare:

• Topsoil • Biological activity

• Subsoil density • Water storage

• Permeability • Suitability for roots

Diagrams: USDA-NRCS Urban Soil Primer

Sustainable

• using a resource in such a way that it is not depleted or permanently damaged

• Horticultural best management practices (BMPs) are operations which establish, maintain, or improve conditions for healthy vegetative growth and environmental quality

• Minimal input – at least in long term

green-gardener.org

ecocomplex.rutgers.edu

http:ecocomplex.rutgers.eduhttp:green-gardener.org

Maintain Good Soil Structure

• Prevent compaction

– limit traffic and other loads, especially when soil is wet

– Promote infiltration

• Prevent erosion to conserve soil and protect natural water bodies and stormwater management infrastructure

• Limited tillage

– Coring to alleviate compaction, improve aeration & infiltration, and incorporate amendments

– Deep ripping when necessary

• Promote biological activity

• Addition of organic matter

Enhance soil organic matter and soil life

• Add organic amendments when starting low

• With adequate initial levels of OM, healthy vegetation will help maintain OM and sustain soil life

• Mulch clippings back into lawn

• A practice and a goal: “maintaining healthy crop” – plants initiate the soil food web

www.northernplains.org

www.lawnsmith.co.uk

Maintain a healthy “crop”

• Maintain dense cover to protect soil surface

• Irrigate during establishment or drought

• Re-establish vegetation when necessary

• Deal with pest outbreaks when necessary

• Off-season care – avoid damage from snowplows, de-icing salts

Soil Test! To manage soil pH and nutrient levels

Conclusions

• Stewardship of soils in sub/urban landscapes will avoid many problems and minimize costs in the long run

• Monitoring and measured management of soils will help develop and sustain successful landscapes

• BMPs often involve prevention of soil degradation: compaction, smearing, bare soil, crusting/sealing, fertility depletion, acidification, erosion – to minimize pollution risks of waterways and help maintain healthy landscapes!

Rutgers Soil Testing Laboratory soiltest@aesop.Rutgers.edu

www.facebook.com/RutgersSoilTestingLab

www.facebook.com/RutgersSoilTestingLabmailto:soiltest@aesop.Rutgers.edu

Structure BookmarksCelebrate! Start with the Soil: The Groundwork for Healthy Plants What is Soil? Components of soil Soil is 3-D! Soil Texture influences… Pores -containing water and/or air Time Nutrient Supply Compaction Conclusions